Three-dimensional semiconductor packages become essential for a higher density and capacity. The 3D semiconductor packaging technology is by thinning semiconductor chips, and stacking them in multilayer structure while providing through-silicon via (TSV) interconnects. Fabrication of such packages requires the steps of thinning a substrate having a semiconductor circuit formed therein by grinding its non-circuit forming surface or back surface, and forming TSV and electrodes on the back surface. In the prior art, prior to the step of grinding the back surface of a silicon substrate, a protective tape is attached to the surface of the substrate opposite to the surface to be ground for preventing the wafer from breakage during the grinding step. Since the protective tape is based on an organic resin film, it is flexible, but has insufficient strength and heat resistance to withstand the TSV forming step and the step of forming interconnects on the back surface.
It is then proposed to bond a semiconductor substrate to a support of silicon or glass, for example, via an adhesive layer. The resulting system is sufficient to withstand the steps of grinding the back surface and forming TSV and electrodes on the back surface. The adhesive layer for bonding the substrate to the support is critical for this system. The adhesive layer must bond the substrate to the support without leaving gaps, be durable enough to withstand the subsequent steps, and eventually allow the thin wafer to be readily released from the support. The adhesive layer is referred herein to as “temporary adhesive layer” or “temporary bonding arrangement” since it is finally removed.
With regard to temporary adhesive layers and removal thereof, Patent Document 1 discloses a layer of an adhesive composition containing a light absorbing agent. Since the adhesive composition may be decomposed by irradiating the adhesive layer with high intensity light, the adhesive layer may be removed from the support. Patent Document 2 discloses a layer of an adhesive composition comprising a heat melting hydrocarbon compound, wherein the layer can be bonded and released in the heat molten condition. The former technology requires an expensive tool such as laser and a longer time of treatment per substrate. The latter technology is simple because of control only by heat, but applicable to a limited range because of poor heat stability at high temperatures in excess of 200° C. These temporary adhesive layers are not adequate to form a layer of uniform thickness on a heavily stepped substrate and to provide a complete bond to the support.
Patent Document 3 discloses the use of a silicone adhesive composition as the temporary bond layer. A substrate is bonded to a support with an addition reaction curable silicone adhesive composition. On removal, the assembly is immersed in an etching solution capable of dissolving or decomposing the silicone resin, whereby the substrate is separated from the support. This method takes a very long time for removal and is applicable to the commercial manufacture process with difficulty.
Also proposed is a temporary adhesive agent which exhibits heat resistance during wafer processing, establishes a satisfactory temporary bond, and enables effective release at normal temperature. With this method, the wafer is released from the support by mechanical peeling via interfacial or cohesive failure of the temporary adhesive agent. Although the wafer and the support can be separated in a relatively simple manner, this method has the risk that the adhesive agent forms particles upon separation, with which the equipment can be contaminated.
Patent Documents 4 and 5 disclose that an antistatic agent is added to adhesives or pressure-sensitive adhesives such as acrylic adhesives and epoxy adhesives to reduce surface resistivity at the adhesive surface. Since the addition of antistatic agent rather adversely affects heat resistance, the resulting adhesive is inadequate as the temporary adhesive in the semiconductor field involving temperature exposure.